<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        body{
            padding:0;
            margin:0;
        }
        .box{
            width: 420px;
            margin:100px auto;
            position:relative;
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            height: 600px;
            background-color:pink;
        }
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            width: 200px;
            height: 200px;
            background-color:lightblue;
            position:absolute;
            left:210px;
            top:0;
        }
    </style>
</head>
<body>
<div class="box">
    <div class="parent"></div>
    <div class="son"></div>
</div>
<script>
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            son.style.display="none";
        },700);
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</script>
</body>
</html>